Stromal Cell-Derived Growth Factor-1 Alpha-Elastin Like Peptide Fusion Protein Promotes Cell Migration and Revascularization of Experimental Wounds in Diabetic Mice

Bioactive nanomaterials kickstart early repair processes and potentiate temporally modulated healing of healthy and diabetic wounds

Slow-healing and chronic wounds represent a major global economic and medical burden, and there is significant unmet need for novel therapies which act to both accelerate wound closure and enhance biomechanical recovery of the skin. Here, we report a new approach in which bioactives that augment early stages of wound healing can kickstart and engender effective wound closure in healthy and diabetic, obese animals, and set the stage for subsequent tissue repair processes. We demonstrate that a nanomaterial dressing made of silk fibroin and gold nanorods (GNR) stimulates a pro-neutrophilic, innate immune, and controlled inflammatory wound transcriptomic response. Further, Silk-GNR, lasered into the wound bed, in combination with exogeneous histamine, accelerates early-stage processes in tissue repair leading to effective wound closure. Silk-GNR and histamine enhanced biomechanical recovery of skin, increased transient neoangiogenesis, myofibroblast activation, epithelial-to-mesenchymal transition (EMT) of keratinocytes and a pro-resolving neutrophilic immune response, which are hitherto unknown activities for these bioactives. Predictive and temporally coordinated delivery of growth factor nanoparticles that modulate later stages of tissue repair further accelerated wound closure in healthy and diabetic, obese animals. Our approach of kickstarting healing by delivering the "right bioactive at the right time" stimulates a multifactorial, pro-reparative response by augmenting endogenous healing and immunoregulatory mechanisms and highlights new targets to promote tissue repair.

Construction of a Collagen-like Protein Based on Elastin-like Polypeptide Fusion and Evaluation of Its Performance in Promoting Wound Healing

In the healing of wounds, human-like collagen (hCol) is essential. However, collagen-based composite dressings have poor stability in vivo, which severely limits their current therapeutic potential. Based on the above, we have developed a recombinant fusion protein named hCol-ELP, which consists of hCol and an elastin-like peptide (ELP). Then, we examined the physicochemical and biological properties of hCol-ELP. The results indicated that the stability of the hCol-ELP fusion protein exhibited a more compact and homogeneous lamellar microstructure along with collagen properties, it was found to be significantly superior to the stability of free hCol. The compound hCol-ELP demonstrated a remarkable capacity to induce the proliferation and migration of mouse embryo fibroblast cells (NIH/3T3), as well as enhance collagen synthesis in human skin fibroblasts (HSF) when tested in vitro. In vivo, hCol-ELP demonstrated significant enhancements in healing rate and a reduction in the time required for scab removal, thereby exhibiting a scar-free healing effect. The findings provide a crucial theoretical foundation for the implementation of an hCol-ELP protein dressing in fields associated with the healing of traumatic injuries.

Alpha-ketoglutaric acid based polymeric particles for cutaneous wound healing

Metabolites are not only involved in energy pathways but can also act as signaling molecules. Herein, we demonstrate that polyesters of alpha-ketoglutararte (paKG) can be generated by reacting aKG with aliphatic diols of different lengths, which release aKG in a sustained manner. paKG polymer-based microparticles generated via emulsion-evaporation technique lead to faster keratinocyte wound closures in a scratch assay test. Moreover, paKG microparticles also led to faster wound healing responses in an excisional wound model in live mice. Overall, this study shows that paKG MPs that release aKG in a sustained manner can be used to develop regenerative therapeutic responses.

Multifunctional Elastin-Like Polypeptide Fusion Protein Coacervates Inhibit Receptor-Mediated Proinflammatory Signals and Promote Angiogenesis in Mouse Diabetic Wounds

Objective: Chronic skin wounds are one of the most devastating complications in diabetic patients due to the formation of advanced glycation end-products (AGEs) resulting from nonenzymatic glycation of proteins and lipids in hyperglycemia. AGEs, upon binding their receptors (RAGEs), trigger proinflammatory signals that impair wound healing in diabetes and contribute to the pathology of chronic skin wounds. Approach: We previously developed a recombinant fusion protein containing the binding domain of RAGE (vRAGE) linked to elastin-like polypeptides (ELPs) that acts as a competitive inhibitor of AGEs, and another ELP fusion protein containing stromal cell-derived factor 1 (SDF1) that promotes revascularization. In this study, we report the effects of protein coacervates incorporating both vRAGE-ELP and SDF1-ELP on wound healing in an in vitro diabetes-mimicking cell culture system, and in in vivo in full-thickness wounds on diabetic mice. Results: The combination of vRAGE-ELP and SDF1-ELP increased cell metabolic activity in AGE-stimulated endothelial cells, promoted in vitro tube formation and accelerated healing in an in vitro cell migration assay. When used in a single topical application on full-thickness excisional skin wounds in diabetic mice, wound closure in the combination groups reached almost 100% on postwounding day 35, compared to 62% and 85% on the same days in animals treated with fibrin gel control and vehicle control consisting of ELP alone. Innovation: To our knowledge, this is the first study that attempts to reverse the AGE-RAGE-mediated signaling as well as to promote cell proliferation and vascularization in one single treatment. Conclusion: The codelivery of vRAGE-ELP and SDF1-ELP has potential for the treatment of diabetic wounds.

Tissue Engineering-Based Strategies for Diabetic Foot Ulcer Management

Significance: Diabetic foot ulcers (DFU) are a mounting problem with the increasingly frail population. Injuries that would otherwise heal are kept open by risk factors such as diabetes, obesity, and age-related conditions, which interferes with the natural wound healing processes. Recent Advances: This review summarizes recent advancements in the field of tissue engineering for the treatment of DFUs. FDA-approved approaches, including signaling-based therapies, stem cell therapies, and skin substitutes are summarized and cutting-edge experimental technologies that have the potential to manage chronic wounds, such as skin printing, skin organogenesis, skin self-assembly, and prevascularization, are discussed. Critical Issues: The standard of care for chronic wounds involves wound debridement, wound dressings, and resolving the underlying cause such as lowering the glycemic index and reducing wound pressure. Current DFU treatments are limited by low wound closure rates and poor regrown skin quality. New adjuvant therapies that facilitate wound closure in place of or in conjunction with standard care are critically needed. Future Directions: Tissue engineering strategies are limited by the plasticity of adult human cells. In addition to traditional techniques, genetic modification, although currently an emerging technology, has the potential to unlock human regeneration and can be incorporated in future therapeutics.

Cytokine conjugates to elastin-like polypeptides

Cytokines are a group of pleiotropic proteins which are crucial for various biological processes and useful as therapeutics. However, they usually suffer from the poor stability, extreme short circulation half-life, difficulty in high-yield and large-scale production and side effects, which greatly restricts their applications. Over the past decades, conjugation of cytokines with elastin-like polypeptides (ELPs), a type of promising biomaterials, have showed great potential in solving these challenges due to ELP's thermal responsiveness, excellent biocompatibility and biodegradability, non-immunogenicity, and ease of design and control at the genetic level. This review presents recent progress in the design and production of a variety of ELP conjugated cytokines for extended circulation, enhanced stability, increased soluble protein expression, simplified purification, improved drug delivery, and controlled release. Notably, the unique thermoresponsive properties of cytokine-ELP conjugates make it possible to self-assemble into micelles with drastically extended circulatory half-life for targeted delivery or to in situ form drug depots for topical administration and controlled release. The challenges and issues in the emerging field are further discussed and the future directions are pointed out at the end of this review.

Combinatorial Use of Therapeutic ELP-Based Micelle Particles in Tissue Engineering

Elastin-like peptides (ELPs) are a versatile platform for tissue engineering and drug delivery. Here, micelle forming ELP chains are genetically fused to three therapeutic molecules, keratinocyte growth factor (KGF), stromal cell-derived growth factor 1 (SDF1), and cathelicidin (LL37), to be used in wound healing. Chronic wounds represent a growing problem worldwide. A combinatorial therapy approach targeting different aspects of wound healing would be beneficial, providing a controlled and sustained release of active molecules, while simultaneously protecting these therapeutics from the surrounding harsh wound environment. The results of this study demonstrate that the conjugation of the growth factors KGF and SDF1 and the antimicrobial peptide LL37 to ELPs does not affect the micelle structure and that all three therapeutic moieties retain their bioactivity in vitro. Importantly, when the combination of these micelle ELP nanoparticles are applied to wounds in diabetic mice, over 90 % wound closure is observed, which is significantly higher than when the therapeutics are applied in their naked forms. The application of the nanoparticles designed here is the first report of targeting different aspect of wound healing synergistically.

Application of elastin-like polypeptide (ELP) containing extra-cellular matrix (ECM) binding ligands in regenerative medicine

Extracellular matrix (ECM) molecules play an important role in regulating molecular signaling associated with proliferation, migration, differentiation, and tissue repair. The identification of new kinds of ECM mimic biomaterials to recapitulate critical functions of biological systems are important for various applications in tissue engineering and regenerative medicine. The use of human elastin derived materials with controlled biological properties and other functionalities to improve their cell-response was proposed. Herein, we reported genetic encoded synthesis of ELP (elastin-like polypeptide) containing ECM domains like RGD (integrin binding ligand) and YIGSR (laminin-selective receptor binding ligand) to regulate cell behaviour in more complex ways, and also better model natural matrices. Thermal responsiveness of the ELPs and structural conformation were determined to confirm its phase transition behaviour. The fusion ELPs derivatives were analysed for mechanical involvement of growth mechanism, regenerative, and healing processes. The designed fusion ELPs promoted fast and strong attachment of fibroblast cells. The fusion ELP derivatives enhanced the migration of keratinocyte cells which of crucial for wound healing. Together it provides a profound matrix for endothelial cells and significantly enhanced tube formation of HUVEC cells. Thus, strategy of using cell adhesive ELP biopolymer emphasizing the role of bioactive ELPs as next generation skin substitutes for regenerative medicine.

Self-assembled elastin-like polypeptide fusion protein coacervates as competitive inhibitors of advanced glycation end-products enhance diabetic wound healing

Chronic and non-healing skin wounds are some of the most significant complications in patients with advanced diabetes. A contributing mechanism to this pathology is the non-enzymatic glycation of proteins due to hyperglycemia, leading to the formation of advanced glycation end products (AGEs). AGEs bind to the receptor for AGEs (RAGE), which triggers pro-inflammatory signals that may inhibit the proliferative phase of wound healing. Soluble forms of RAGE (sRAGE) may be used as a competitive inhibitor of AGE-mediated signaling; however, sRAGE is short-lived in the highly proteolytic wound environment. We developed a recombinant fusion protein containing the binding domain of RAGE (vRAGE) linked to elastin-like polypeptides (ELPs) that self-assembles into coacervates at around 30-31 °C. The coacervate size was concentration and temperature-dependent, ranging between 500 and 1600 nm. vRAGE-ELP reversed several AGE-mediated changes in cultured human umbilical vein endothelial cells, including a decrease in viable cell number, an increase in levels of reactive oxygen species (ROS), and an increased expression of the pro-inflammatory marker, intercellular adhesion molecule-1 (ICAM-1). vRAGE-ELP was stable in elastase in vitro for 7 days. When used in a single topical application on full-thickness excisional skin wounds in diabetic mice, wound closure was accelerated, with 90% and 100% wound closure on post-wounding days 28 and 35, respectively, compared to 62% and 85% on the same days in animals treated with vehicle control, consisting of ELP alone. This coacervate system topically delivering a competitive inhibitor of AGEs has potential for the treatment of diabetic wounds.

Emerging Role of Elastin-Like Polypeptides in Regenerative Medicine

Significance: Wound dressing based on naturally derived polymer provides a useful platform for treatment of skin injuries. Owing to the high mechanical strength and tunable structural and physicochemical properties of human elastin-like polypeptides (ELPs), they may be used as excellent materials for fabricating biocompatible scaffolds and other products for wound management. Recent Advances: Designing recombinant ELPs mimicking natural elastin to fabricate synthetic polymers suitable for human health care has generated significant interest. ELP-based cell-adhesive biopolymers have been used as an alternative for successful sutureless wound closure due to the physicochemical characteristics of the extracellular matrix. Critical Issues: Different systems of ELPs are being developed in the form of scaffolds, films, hydrogels, photo-linkable sheets, and composites linked with various types of growth factors for wound healing application. However, optimizing the quality and safety attributes for specific application needs designing of recombinant ELPs with structural and functional modifications as needed for the intervention. Future Direction: Chronic wounds are difficult to treat as the wound repair process is interrupted by conditions such as excessive inflammation, impaired extracellular matrix formation, and persistent infections. Conventional therapies such as skin substitutes or autologous skin grafts, in many cases, are unable to reestablish tissue homeostasis and proper healing. The development of innovative materials could induce a better regenerative healing response. In this study, we are reviewing different types of elastin-based materials for wound care application and their future prospects in regenerative medicine.

Nanotechnology Approaches in Chronic Wound Healing

Significance: The incidence of chronic wounds is increasing due to our aging population and the augment of people afflicted with diabetes. With the extended knowledge on the biological mechanisms underlying these diseases, there is a novel influx of medical technologies into the conventional wound care market. Recent Advances: Several nanotechnologies have been developed demonstrating unique characteristics that address specific problems related to wound repair mechanisms. In this review, we focus on the most recently developed nanotechnology-based therapeutic agents and evaluate the efficacy of each treatment in in vivo diabetic models of chronic wound healing. Critical Issues: Despite the development of potential biomaterials and nanotechnology-based applications for wound healing, this scientific knowledge is not translated into an increase of commercially available wound healing products containing nanomaterials. Future Directions: Further studies are critical to provide insights into how scientific evidences from nanotechnology-based therapies can be applied in the clinical setting.

Self-Assembled Nanomaterials for Chronic Skin Wound Healing

Significance: Chronic wounds are one of the major burdens of the U.S. health care system with an annual cost of $31.7 billion and affecting an estimated 2.4-4.5 million people. Several underlying molecular and cellular pathophysiological mechanisms, including poor vascularization, excessive extracellular matrix (ECM) degradation by proteases, decreased growth factor activity, and bacterial infection can lead to chronic wounds. More effective wound therapies need to address one or more of these mechanisms to significantly advance wound care. Recent Advances: Self-assembled nanomaterials may provide new therapeutic options for chronic wound healing applications as those materials generally exhibit excellent biocompatibility and can bear multiple functionalities, such as ECM-mimicking properties, drug delivery capabilities, and tunable mechanics. Furthermore, self-assembled nanomaterials can be produced at low cost, and owing to their ability to self-organize, generate complex multifunctional structures that can be tailored to the varying sizes and shapes of chronic wounds. Self-assembled nanomaterials have been engineered to serve as wound dressings, growth factor delivery systems, and antimicrobials. Critical Issues: As there are many different types of self-assembled nanomaterials, which in turn have different mechanisms of self-assembly and physiochemical properties, one type of self-assembled nanomaterials may not be sufficient to address all underlying mechanisms of chronic wounds. However, self-assembled nanomaterials can be easily tailored, and developing multifunctional self-assembled nanomaterials that can address various targets in chronic wounds will be needed. Future Directions: Future studies should investigate combinations of various self-assembled nanomaterials to take full advantage of their multifunctional properties.

Fabricating a novel HLC-hBMP2 fusion protein for the treatment of bone defects

Treating serious bone trauma with an osteo-inductive agent such as bone morphogenetic proteins (BMPs) has been considered as an optimized option when delivered via a collagen sponge (CS). Previous works have shown that the BMP concentration and release rate from approved CS carriers is difficult to control with precision. Here we presented the fabrication of a recombinant fusion protein from recombinant human-like collagen (HLC) and human BMP-2 (hBMP2). The fusion protein preserved the characteristic of HLC allowing the recombinant protein to be expressed in Yeast (such as Pichia pastoris GS115) and purified rapidly and easily with mass production after methanol induction. It also kept the stable properties of HLC and hBMP2 in the body fluid environment with good biocompatibility and no cytotoxicity. Moreover, the recombinant fusion protein fabricated a vertical through-hole structure with improved mechanical properties, and thus facilitated migration of bone marrow mesenchymal stem cells (MSCs) into the fusion materials. Furthermore, the fusion protein degraded and released hBMP-2 in vivo allowing osteoinductive activity and the enhancement of utilization rate and the precise control of the hBMP2 release. This fusion protein when applied to cranial defects in rats was osteoinductively active and improved bone repairing enhancing the repairing rate 3.5- fold and 4.2- fold when compared to the HLC alone and the control, respectively. There were no visible inflammatory reactions, infections or extrusions around the implantation sites observed. Our data strongly suggests that this novel recombinant fusion protein could be more beneficial in the treatment of bone defects than the simple superposition of the hBMP2/collagen sponge.

Stromal cell-derived factor loaded co-electrospun hydrophilic/hydrophobic bicomponent membranes for wound protection and healing

Chronic wounds are one of the key concerns for people with diabetes, frequently leading to infections and non-healing ulcers, and finally resulting in the amputation of limbs/organs. Stromal cell-derived factor 1 (SDF1) is a major chemokine that plays a significant role in tissue repair, vascularization, and wound healing. However, the long-term sustained delivery of SDF1 in a chronic wound environment is a great challenge. In order to facilitate the sustained release of SDF1 in diabetic wounds, it could be incorporated into wound-healing patches. Herein, we report the fabrication of a hydrophilic/hydrophobic bicomponent fiber-based membrane, where SDF1 was encapsulated inside hydrophilic fibers, and its applicability in wound healing. A co-electrospinning technique was employed for the fabrication of polymeric membranes where PVA and PCL form the hydrophilic and hydrophobic components, respectively. Morphological analysis of the developed membranes was conducted via scanning electron microscopy (SEM). The mechanical strength of the membranes was investigated via uniaxial tensile testing. The water uptake capacity of the membranes was also determined to understand the hydrophilicity and exudate uptake capacity of the membranes. To understand the proliferation, viability, and migration of skin-specific cells in the presence of SDF1-loaded membranes, in vitro cell culture experiments were carried out using fibroblasts, keratinocytes, and endothelial cells. The results showed the excellent porous morphology of the developed membranes with distinguishable differences in fiber diameters for the PVA and PCL fibers. The developed membranes possessed enough mechanical strength for use as wound-healing membranes. The co-electrospun membranes showed good exudate uptake capacity. The controlled and extended delivery of SDF1 from the developed membranes was observed over a prolonged period. The SDF1-loaded membranes showed enhanced cell proliferation, cell viability, and cell migration. These biocompatible and biodegradable SDF1-loaded bicomponent membranes with excellent exudate uptake capacity, and cell proliferation and cell migration properties can be exploited as a novel wound-dressing membrane aimed at chronic diabetic wounds.

Macrophage modulation by polymerized hemoglobins: Potential as a wound-healing therapy

Chronic skin wounds are hypoxic and are stalled in a pro-inflammatory state. Hemoglobin (Hb)-based oxygen carriers have shown potential in increasing oxygen delivery to aid wound healing. Macrophages also take up Hb, thus altering their phenotype and the regulation of inflammation. Herein, we compared the effect of Hb and polymerized Hbs (PolyHbs) on the phenotype of human macrophages. Macrophages were incubated with Hb or different forms of PolyHbs, and the inflammatory secretion profile was analyzed. PolyHbs were produced by polymerizing Hb in the relaxed (R) or tense (T) quaternary state and by varying the molar ratio of the glutaraldehyde crosslinking agent to Hb. Hb decreased the secretion of most measured factors. PolyHb treatment led to generally similar secretion profiles; however, Hb had more similar trends to R-state PolyHb. Ingenuity pathway analysis predicted positive outcomes in wound healing and angiogenesis for T-state PolyHb prepared with a 30:1 (glutaraldehyde:Hb) polymerization ratio. When tested in diabetic mouse wounds, T-state PolyHb resulted in the greatest epidermal thickness and vascular endothelial CD31 staining. Thus, the effects of PolyHb on macrophages are affected by the polymerization ratio and the quaternary state, and T-state PolyHb yields secretion profiles that are most beneficial in wound healing.

Bioactive scaffolds based on elastin-like materials for wound healing

Wound healing is a complex process that, in healthy tissues, starts immediately after the injury. Even though it is a natural well-orchestrated process, large trauma wounds, or injuries caused by acids or other chemicals, usually produce a non-elastic deformed tissue that not only have biological reduced properties but a clear aesthetic effect. One of the main drawbacks of the scaffolds used for wound dressing is the lack of elasticity, driving to non-elastic and contracted tissues. In the last decades, elastin based materials have gained in importance as biomaterials for tissue engineering applications due to their good cyto- and bio-compatibility, their ease handling and design, production and modification. Synthetic elastin or elastin like-peptides (ELPs) are the two main families of biomaterials that try to mimic the outstanding properties of natural elastin, elasticity amongst others; although there are no in vivo studies that clearly support that these two families of elastin based materials improve the elasticity of the artificial scaffolds and of the regenerated skin. Within the next pages a review of the different forms (coacervates, fibres, hydrogels and biofunctionalized surfaces) in which these two families of biomaterials can be processed to be applied in the wound healing field have been done. Here, we explore the mechanical and biological properties of these scaffolds as well as the different in vivo approaches in which these scaffolds have been used.